Machine learning applied to single-shot x-ray diagnostics in an XFEL

Due to the stochastic SASE operating principles and other technical issues the output pulses are subject to large fluctuations, making it necessary to characterize the x-ray pulses on every shot for data sorting purposes. We present a technique that applies machine learning tools to predict x-ray pulse properties using simple electron beam and x-ray parameters as input. Using this technique at the Linac Coherent Light Source (LCLS), we report mean errors below 0.3 eV for the prediction of the photon energy at 530 eV and below 1.6 fs for the prediction of the delay between two x-ray pulses. We also demonstrate spectral shape prediction with a mean agreement of 97%. This approach could potentially be used at the next generation of high-repetition-rate XFELs to provide accurate knowledge of complex x-ray pulses at the full repetition rate. I. INTRODUCTION X-ray free-electron lasers (XFELs) 1-3 are emerging as one of the most versatile tools in x-ray research, becoming widely used by the scientific community, as well as industry, in many fields including physics, chemistry, biology, and material science. Their brightness, coherence, tun-ability, and ability to generate pairs of few-fs multicolor pulses for pump-probe experiments 4-7 make them ideal sources to perform diffract-before-destroy imaging 8, resonant x-ray spectroscopy 9, and a range of time resolved measurements of picosecond to few-femtosecond dynamics in molecules and atoms 10-16 . A drawback to XFELs is their current poor stability. XFELs are driven by single-pass electron linear accelerators (LINAC) typically several hundred meters in length.